Since 5-hydroxy-1H-imidazole-4-carboxamide (henceforth also referred to as Compound A) or a salt thereof, or a hydrate thereof has a potent carcinostatic action, it is a medically useful compound as an anticancer agent (Patent document 1). In particular, it is an anticancer agent that exhibits a potent efficacy against solid carcinomas, against which chemotherapy has conventionally been considered difficult, and is a highly safe anticancer agent that shows less side reactions, and thus it is a compound of which clinical applications are expected in a wide range of dosage forms such as oral agent, injection, ointment, and suppository. The dosage form generally most preferred by patients is tablet (Non-patent document 1).
Compound A has a characteristic that it is easily discolored by oxygen, heat, light, or the like, and when it is made into, for example, an oral preparation, it is affected by interactions of coexisting excipient, and thus tends to show further notable discoloration (Patent document 2).
So far, as a means for preventing such discoloration concerning pharmaceutical preparation design, a method of using a sulfur compound is known (Patent document 3). Further, as a means for preventing discoloration of Compound A, there is known a method of coexisting a solid preparation of Compound A and a commonly used self-activating type deoxidant or deoxidating and carbon dioxide gas-generating agent is known (Patent document 2).